1. Field of the Invention
This invention relates to sources of illumination of constant color temperature and intensity.
2. Description Relative to the Prior Art
In the manufacture and use of photographic materials, such as film or paper, it is necessary to know how the film or paper responds to light. More particularly, it is necessary to know how the film or paper responds to a range of intensities of light at each of a range of different wavelengths. To make meaningful tests, it is necessary to have known intensities at known wavelengths. It is known to use as a source of illumination for such tests, a source of white light which is manufactured at constant brightness, and to use filters to select wavelengths and intensities of exposing illumination in a plurality of sequential tests.
However, the need has been recognized for a source of illumination which has superior constancy of color temperature and intensity, so that the tests on film can be more accurate.